1. Field of the Invention
The present invention generally relates to joint filler compositions, and more particularly to a joint filler composition that fills a joint part between adjacent base members (or furrings) in order to make a height of the joint part approximately the same as that of a surface of the base members, when performing an interior finishing work on an inner wall or a ceiling of a building, for example.
A joint filler composition may sometimes be referred to as a joint filling material, a joint sealing material, or a joint sealer.
2. Description of the Related Art
When performing the interior finishing work of the building, a plurality of base members, such as plaster boards, plywoods, calcium silicate boards, and the like, are arranged and fixed at predetermined positions. Then, a joint filler composition is filled into a joint part between the adjacent base members. After a job-site setting until the joint filler composition dries and sets (or hardens), the joint part is sanded and smoothened in order to make the surface of the joint filler at the joint part match the surface of the adjacent base members, that is, make the surfaces of the joint part and the adjacent base members flush. Thereafter, a wall paper or the like is adhered on the flush surface, in order to finish the inner wall or the ceiling of the building.
The joint part is treated in the above described manner for the following three reasons (1)-(3), for example.                (1) To eliminate a stepped part or a gap at the joint in order to hide the joint;        (2) To reinforce the joint in order to prevent cracks from forming; and        (3) To fill the joint and improve heat resistance and sound insulation.        
The joint filler composition may generally be categorized into a drying type and a setting type.
An example of the drying type joint filler composition is proposed in a Japanese Published Utility Model Application No. 58-35799. The proposed joint filler composition includes calcium carbonate as a base material, mixed with a binder, such as stone powder and a resin bonding agent. The proposed joint filler composition may be coated with ease, and a satisfactory surface finishing may be obtained. Because the drying type joint filler composition does not cure unless dried, the drying type joint filler composition may be prepared in the form of a paste at the manufacturer and forwarded in a container, such as a can, a cartridge, and the like, so that it is unnecessary to mix material and water at the construction site. However, after the drying type joint filler composition is coated and dried, the joint filler composition contracts, and the so-called depression may occur. The shrinkage of the joint filler composition may cause cracks to form. For these reasons, the drying type joint filler composition is mainly used in the finishing stage in which the coating thickness is relatively thin.
On the other hand, examples of the setting type joint filler composition are described in a Japanese Published Patent Application No. 59-19059 and a Japanese Laid-Open Patent Application No. 55-144459. The proposed joint filler compositions include hemihydrate gypsum or hemihydrate plaster as a base material, mixed with a bonding agent and other additives. Because the proposed joint filler compositions include as the base material, hemihydrate plaster that expands by hydration curing, the amount of shrinkage after the curing is smaller compared to that of the drying type joint filler composition. For this reason, the setting type joint filler composition is often used for the undercoating (or base coating) that requires a relatively thick coating, because the shrinkage or the so-called depression is relatively small. However, even in the case of the setting type joint filler composition, when mixing water is absorbed by the undercoating before the joint filler composition undergoes the hydration setting, the joint filler composition coated at the joint part contracts and the shrinkage or the so-called depression occurs.
Accordingly, both types of the joint filler composition described above contract, and the surface of the joint filler composition filled into the joint part of the undercoatings (or base members) and the surfaces of the base undercoatings do not match, to thereby form an undulation (or concavo-convex). When the wall paper is adhered over the undercoatings having the joint part filled by the joint filler composition, the undulation underneath also appears on the wall paper and damages the external appearance of the wall paper. For this reason, the joint filler composition must be coated again and dried again and such coating and drying must be repeated until the surface of the joint filler composition filled into the joint part of the undercoatings and the surfaces of the base undercoatings approximately match. The operation to coat and dry the joint filler composition again is a troublesome operation, and in addition, each single coating requires a corresponding drying time. As a result, when the coating and drying of the joint filler composition need to be repeated, the time of completion is delayed.
In order to minimize the above described problems, a joint filler composition mixed with a lightweight aggregate including air within particles, such as hollow particles, has been proposed. An example of such a joint filler composition that reduces the shrinkage or the so-called depression forms an undercoating adjusting agent including an inorganic filler such as gypsum-calcium carbonate, a lightweight filler such as a hollow balloon perlite vermiculite, and a liquid binder having an emulsion resin as a principal component, is proposed in a Japanese Laid-Open Patent Application No. 2001-40277.
However, a mixture amount of the hollow particles must be increased in order to reduce the shrinkage or the so-called depression, and the operation of manually coating the joint filler composition by a jig such as a finishing knife takes more time as the amount of the hollow particles increases. The operation of coating the joint filler composition thus becomes more troublesome to perform. For these reasons, the amount of the hollow particles mixed in the joint filler composition is desirably limited to a predetermined amount that does not considerably deteriorate the efficiency of coating the joint filler composition, and consequently, the shrinkage or the so-called depression may not be reduced sufficiently.
Therefore, according to the conventional joint filler compositions, it is difficult to simultaneously enable coating of the joint filler composition with a satisfactory workability and sufficiently reduce the shrinkage or the so-called depression.